You could also more actively "keep" the desired fields.

sub loadFileToHashRef
{
  my $xmlRef      =       $xml->XMLin($_[0]);
  
  # Clean our hash
  for my $textRef ( @{$xmlRef->{sms}} )
    {   
      %{$textRef} = map { $_ => $textRef->{$_} } @keysToKeep;
    }   
  
  # Return our hash ref
  return $xmlRef;
}
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If they didn't exist in the XML, you will get some undefs.